Reproducibility of Glutamate, Glutathione, and GABA Measurementsin vivoby Single-Voxel STEAM Magnetic Resonance Spectroscopy at 7-Tesla in Healthy Individuals

Background and Purpose Derangements in brain glutamate, glutathione, and gamma-amino butyric acid (GABA) are implicated in a range of neurological disorders. Reliable methods to measure these compounds non-invasivelyin vivoare needed. We evaluated the reproducibility of their measurements in brain regions involved in the default mode network using quantitative MRS at 7-Tesla in healthy individuals. Methods Ten right-handed healthy volunteers underwent 7-Tesla MRI scans on 2 separate days, not more than 2 weeks apart. On each day two scanning sessions took place, with a re-positioning break in between. High-resolution isotropic anatomical scans were acquired prior to each scan, followed by single-voxel(1)H-MRS using the STEAM pulse sequence on an 8 mL midline cubic voxel, positioned over the posterior cingulate and precuneus regions. Concentrations were corrected for partial-volume effects. Results Maximal Cramer-Rao lower bounds for glutamate, glutathione, and GABA were 2.0, 8.0, and 14.0%, respectively. Mean coefficients of variation within sessions were 5.9 +/- 4.8%, 9.3 +/- 7.6%, and 11.5 +/- 8.8%, and between sessions were 4.6 +/- 4.5%, 8.3 +/- 5.7%, and 9.2 +/- 8.7%, respectively. The mean (+/- SD) Dice's coefficient for voxel overlap was 90 +/- 4% within sessions and 86 +/- 7% between sessions. Conclusion Glutamate, glutathione, and GABA can be reliably quantified using STEAM MRS at 7-Tesla from the posterior cingulate and precuneus cortices of healthy human subjects. STEAM MRS at 7-Tesla may be used to study the metabolic behavior of this important resting-state hub in various disease states.